1. Field of the Invention
The present invention relates to a method of correcting a measurement error in which when electrical characteristics of an electronic component under test having a plurality of ports are measured using a test instrument with the electronic component under test mounted on a production test fixture, a production test fixture measurement value of the electronic component under test using the production test fixture is corrected to electrical characteristics that are assumed to be obtained when one of the test instrument and another test instrument considered equivalent to the test instrument in measurement performance characteristic measures the electronic component under test in the mounted state thereof on a standard test fixture that results in a measurement result of electrical characteristic of the electronic component different from the measurement result of electrical characteristic of the electronic component provided by the production test fixture. The present invention also relates to an electronic component characteristic measurement apparatus performing the measurement error correction method.
2. Description of the Related Art
An SOLT calibration method is carried out to remove the effect of an error of a measurement system from a measurement value. A standard device having a true physical value of an electrical characteristic (such as a scattering coefficient) identified beforehand is prepared. Here, a coaxial electronic component having the true physical value of the electrical characteristic at an extreme limit is used as a standard device. The coaxial electronic component is used as a standard device because it is relatively easy to identify the true physical value of the electrical characteristic in the coaxial electronic component having the extreme value in electrical characteristic. The true physical values in the electrical characteristics of the coaxial electronic component in electrical states such as an open circuit, short circuit, and termination exhibit extreme values. Such a coaxial electronic component is used as a standard device. Determination of the true physical value of the electrical characteristic of the electronic component such as the coaxial electronic component is here referred to as identifying the true physical value.
Returning to the discussion of the SOLT calibration. A standard device prepared is connected to the end of a coaxial cable with the other end connected to one or a plurality of connection ports arranged on a measurement apparatus. Electrical characteristics of the standard device are measured in this setup. With the standard device removed, the terminals of the coaxial cables (the ports on the measurement apparatus) are connected to each other (in a through connection). The electrical characteristics of the cable are then measured. An error factor up to the ends of the coaxial cable is identified from the electrical characteristics in a state with the standard device connected. The effect of an error is removed from the measured electrical characteristics by identifying the error factor. The electrical characteristics of a coaxial electronic component connected to the ends of the coaxial cable are thus calculated. The end of the coaxial cable serves as a calibration plane.
A correspondence between a measurement value and a true physical value of the standard device is calculated (the error factor of the standard device is identified). When electrical characteristics of an actual specimen are measured, the measurement value is corrected based on the calculated correspondence (the effect of the error factor is removed using calculation). The calculation of the correspondence and the correction of the measurement value based on the correspondence (the identification of the error factor and the removal of the error factor through calculation) are referred to as a calibration. The SOLT calibration is one of such calibrations.
An electronic component having no coaxial connector (referred to as a non-coaxial electronic component), such as a surface mounted electronic component, needs to be subjected to the above calibration when electrical characteristics of such a component are measured. A coaxial cable connected to a connection port of a measurement apparatus is connected to a non-coaxial electronic component through a fixture. The fixture has a coaxial connector which is to be connected to the coaxial cable. The fixture is connected with the coaxial connector that is connected to the coaxial cable. The measurement apparatus measures the electrical characteristics of the non-coaxial electronic component mounted on the fixture connected to the coaxial cable.
A standard device is required in principle to calibrate the non-coaxial electronic component. It is practically impossible to produce a standard device for these non-coaxial electronic components. This is because the identification of the true physical value of a standard device other than coaxial types is extremely difficult. If the non-coaxial electronic component is calibrated in a state with a non-coaxial standard device unemployed, a calibration plane becomes the end of the coaxial cable regardless of a fixture attached to the coaxial cable. For this reason, the non-coaxial electronic component is measured in electrical characteristics with the non-coaxial electronic component mounted on the fixture employed at no calibration plane.
There is a possibility that an error takes place in the fixture. The electrical characteristics of the non-coaxial electronic component are identified without paying attention to an error factor caused by the fixture or the error factor due to the fixture is estimated through calculation based on physical dimensions of the fixture. The estimated error factor of the fixture is removed from measured electrical characteristics through calculation. The precision of calibration is thus heightened during measurement of the non-coaxial electronic component. (see, for example, Agilent Technologies 8720ES User's Guide p. 7-37 to p. 7-51.)
A conventional art for calibrating a non-coaxial electronic component during a particular measurement does not provide necessarily a high calibration accuracy. As discussed above, a calibration plane of a measurement apparatus (mainly, a network analyzer) is forced to be at a coaxial face such as the end of a coaxial cable. A measurement apparatus tests a electronic component connected through a calibration plane subject to restrictions. However, a non-coaxial electronic component is not directly connected to the coaxial face (a calibration plane). For measurement, a non-coaxial electronic component is connected to the measurement apparatus through a fixture which is a sort of a transmission line. Each fixture has its own characteristics, and it is difficult to make uniform characteristics among a plurality of fixtures. When characteristics of the non-coaxial electronic component are measured through the fixture, an error unique to each fixture naturally occurs. This creates variations in measurement results, thereby leading to a degradation in calibration accuracy.
Making uniform characteristics among a plurality of fixtures in a non-coaxial electronic component having three ports (such as a duplexer) is even more difficult, and fixtures are not practicable.
Electronic components working on a balanced signal in high frequency regions rather than on an unbalanced signal are currently increasing in number. A balanced signal is transmitted as two signals different in phase by 180° and a received signal is picked up at a receiver side of the balanced signal as a difference between the two signals. Because of its excellent noise immunity over a conventional unbalanced signal, the balanced signal is preferably currently used. Since a single signal is transmitted as two signals in the balanced signal mode, one balanced port corresponds to two unbalanced ports. For example, a filter having balanced input and output is a two-port device, but practically corresponds to an unbalanced device having four ports. In fact, the filter having the balanced input and output is provided with four input and output terminals in addition to a ground terminal.
With more and more electronic components becoming balanced, the number of ports of non-coaxial electronic components such as surface mounted components is expected to increase. There is a need for a relative correction method (calibration method) which works with these types of electronic components, provides high calibration accuracy, and satisfies multi-port requirements.